Automatic tuning control circuit



March 21, 1950 M. G. NICHOLSON, JR 2,501,575

AUTOMATIC TUNING CONTROL CIRCUIT Filed Fb. 8, 1944 nlml: 1"-

, ATTORNEY Patented Mar. 21,` 1950 UNITED STATES PATENToFFIcE lAUTOMATIC TUNING CONTROL CIRCUIT Madison G. Nicholson, Jr., snydor, N.Y., as-

signor to Colonial Radio Corporation, Buffalo, N. Y.

Application February 8, 1944, Serial No. 521,511

(Cl. Z50-40) Claims. l

This invention relates to an automatic tuning control circuit, andmoreparticularly to automatic crystal controlled radio transmitters orreceivers, although it will be understood that my invention may beapplied in other apparatus where automatic tuning of a circuit to anyone of a series of predetermined frequencies is desired. Various formsof circuits of this type have been described and claimed in a 3o-pendingapplication of William S. Wneld, Serial No. 463,775, led October 29,1942. In apparatus of this type the circuits are automatically tuned todesired frequencies determined by crystals, and do not involve thesetting of mechanical elements, such as pins, contactors, selectingcams,

rocker bars, or the like.

In such apparatus there may be provided a variable tuninginstrumentality, such as a condenser or variometer operated by anelectric vmotor through a suitable form of reduction gearing. Since theapparatus is particularly useful in airborne radios where space andweight requirements are strict, and since continuous operation is notrequired, the motor being in operation only when the tuning of theapparatus is equipment and parts.`v y

changed, it is customary to use a motor which is somewhat smaller andof` lighter construction than would be necessary for continuousoperation. This apparatus, according to the application above referredto, is arranged so that the motor circuit is closed in the absence of avoltage in the circuit to be tuned and is opened when the voltage in thecircuit rises to a predetermined level, so that when the circuit reachesresonance the motor stops operating. On the other hand, ii for anyreason this predetermined voltage is not generated the motor willcontinue to operate indefinitely, driving the tuning instrumentalityrepeatedly through the tuning cycle. This is likely to produceoverheating of the motor and may even burn it out. l v

In accordance with this invention I have provided a circuit which may besaid to provide an automatic test of operating conditions once eachtuning cycle while the motor is in operation. If this test shows thatthe apparatus is functioning properly, the circuit will permitcontinuing operation of the motor for another cycle. If not, the motoris stopped and remains stopped until the trouble is found and remedied.

It is an object of this invention to provide apparatus which willprevent sustained overloading and burnout of the driving motor, whichwould occur on continuous operation.v

It is a further object Of this invention to provide apparatus which willstop the operation of the driving motor. in casel .of certain failure inthe associated apparatus, which would otherwise cause the apparatus .to:continually vary its tuning. y f

It is stilla further` object of this invention to provide such apparatuswith a minimum of added It is still a further object of this inventionto provide apparatus of the class described which will stop operation ofthetuning motor in case the crystal control elements become defective orremoved from their. sockets or in case of other trouble which preventsthe resonant circuit from building up a voltage. Y Still other objectsandjadvantages. of my invention will be apparentfrom the specification.In the drawing, the single figure is a Icircuit diagram of one form ofapparatus in accordance with my invention.

Referring now more particularly to the drawing, I represents a Workcircuit which may be a resonator circuit such as thev Well-known crystaland tube oscillator' l5 variably tuned bycondenser 9 connected throughleads 26 and 21 or other tuning instrumentality. Customarily, a numberof crystals l 6,11, I8 are provided, associated with the work circuit|,f'and some 'form of selecting means la. by which Athe operator mayconnect the desired crystal 'into the circuit to X the frequency of thevwork circuit. The apparatus may be a radio transmltter or, receiver oranother form of circuit in which it is desired'to provide tuning to anyone of a number of previously selected frequencies.

The tuning instrumentality herein referred to as a condensen although itmay be any other instrumentality,' may 'be driven by any `suitable powermeans, such as motor l, through suitable reduction gearing 1a, and thecondenser S'may be the means for 'varying the tuning of work circuit l.In order'tocontrol the motori by means of the voltage kin thel workcircuit I., the voltage derived from this circuit may berectifled andpassed through a resistance included in a unit 2, and the resultingvoltage drop may vbe'iinpressed between cathode 3a vand controlelectrode3b of tube 3. Connected to the anode 3c thereof, there may beprovided the energizing Winding of relay 4, having armature 4a, anenergized-position fixed contact 4b, and a deenergized-position fixedcontact 4c. The relay 4 controls the opening and closing of the circuitof motor 'l through source l0, through:` connections made through camswitch l5y driven bycam 8-Y synchronized with "treiuatsrstutejttttrti ne'15g-,tire sitter e t condenser 9, and having a cam segment Sacorresponding to only a relatively small part of the tuning cycle.

The came switch comprises the two movable contacts 6a and 6b, thecontact 6a cooperating with a rst stationary contact 6c and a secondstationary contact 6d while the contact 6b similarly cooperates with afirst stationary contact Be and a second stationary contact 8f. Movablecontacts Sa and 6b are mechanically connected together, as indicated bythe dotted lines, for operation in unison and both n'age their r'e'-spective xed contacts 6d and Ef at all times during the tuning cycleeicept whennth'ey are moved to close their other yrespective iii'rdcontacts 6c and Be by the passage of cam segment 8a, under them.

Connections may be provided between fixed contact 4c and xed contact 6cthrough lead 20; between iixed contact 4band fixed contact 51 through'lead 21; between notatie ttr'rtact et and ctritrti eiettrue it throughieee `21g; aire 'between rectier 'and resistance l unit `2 and fatedcontact Gf through le'ad 23. Fiird contact 6e may be connectedthroughwaseries resistor -II d shunttond'esler (2' and through leas 2tto t "e control grid I5gI of thevvosjcillator' I5, which ma bea part ofwork circit i .Q Y

Do'vable Contact 4d is gliirdj'ed and movable contact 'Ea is connectedtonne :side of lthe iiibt'or circuit, the 'other side of whichais.connected tl'irfngh a Suitable power sor'c'ze I0 to ground. The motorenergizing circuit is thus completed in either 'of two ways. The tirstof thesereduirs that the relay 4 shall not energ'ied by the control tube3, so, that the relay conta'ctfsjll' and fit are closed, arid furtherrequires that the `cam segment Ba shall movemth'e contact Gu 'to`Aengage its liked 'Contact '6o. The motor circuit is then completedfrom the source I0 through the closed cam-switch contacts 'B and 6ta,conductor 20, and 'closed relay contacts H and le. The second manner bywhich the motor Vei-i'er'giaing circuit is completed requires that therelay 4 be energized by the` control tube 3,vto close the relay contacts4a and 4b, and further requires 'thatthe cam 8 operate the movableswitch-contact 6a, to close vits stationary contact 6d. -In this casethe motor `circuit is completed from the source l0 through the-camlswitch 'closed contacts 6a, 6d, the conduotor 2 I', and the clsedrelay contacts 4a and 4b.

It will be observed that when th'e cam `switch is not actuated by thecam segment 8o, the volt- `ag'e derived from the work lcircuit I throughrectifer and 'resistance nit 2 is impressed upon the control 'electrode3b of tube 3 through fixed Icori- -tact '6j and movable contact 6b. When'cam switch Bb is actuated by 'cam segment im, the control electrode 3b'ci tube 3 is connected to the 'switch 'contacts '6b and 6, the resistor'I 1, and the frt will be 'opstarten that during the time tue control'electrode "3U "6i 'tube 331s iectd tothe siting circuit fis 'compi-testy tnt uteritrgieeu operating 'teireititn er the reiay t 'the 'retten'that the tait segrfrent sa strette nostre ci the cam-switch tttatts taata et. 'it 'ru-11 fui-tirer te tb'servea *that during the titre the'centrer electrode "3b of tube 13 `i"s conne' e'd tothe tion of therelay 4 since the cam 8 now closes the cam-switch contacts 6a and 6d.

With the foregoing description of the apparatus and connections in mind,the operation of the circuit will be readily understood. Assuming thatthe apparatus is operating on one predetermined frequency and theoperator desires to shift t'o another `f'rer'iuency, he Imay remove theoperatin'g crystal from its socket and insert the new crystal, or ifselecting switches are provided as shown, he may operate the selectingswitch to select the new frequency. Upon disconnection or removal of theiirst crystal, the output energy of the work` circuit drops to zero, thebias voltage on tube 3 drops t'o zero, plate current increases, andcontact 4d is closed against contact 4b.

If cai'n switch 6 is positioned at this time to close its contacts Ea,6d and 6b, 5f, which it is except for a small part of the tuning cycle,then the motor circuit is closedthrough contact 6d and Sa and the 'motoroperates, var-yimg the tuning of the Awork circuit I through condenser9. When the work circuit b'eciiies resonant to the new frequency, itbegins to deliver output voltage, the bias voltage impressed on tube 3from the recter and resistance 2 reduces the plate current of tube 3 tothe Vpoint 'where the lrelay 4 'opens and contact la moves out ofengagement with Contact 4h and into engagement with con- 'tact 4c, thusinterrupting the `ni'c'utor circuit- The apparatus will remain tuned totlri'e neit7 frequency until the operator changes it again, or until thework circuit 'stops 'd'elve1`"`1n"gl 'a 'voltage for 'some other reason.l

It the crystal 'or oscillator should suddenly become inoperative, thework circuit `v'rould stop delivering voltage to the rbtier andresistance 2, bias 'voltage on tube 3 would be reduced so that relay 4would again be energized, 'and contact -lI-a 'would move into engagementwith 'contact 4b, thus closing the Vmotor 'circuit and operating thetuning I'condenser 9. v'This 'condition would contiue, resulting asaboveV explained in possible overheati'n'g or burnout of 'the motor 1,but for the operation o the can operated switch 6. At o' point in thetuning cycle, the 'ca'm' segment 8a actuat'es th switch "6, 'closingmovable 'contact 6a `agaist3ie`d Contact 5c 'and movable Contact '6hagainst fixed contact Ec 'as 'already explained.

With Contact 4c against contact 4b as last described, the cam actuationof switch 6 momentarily opens the motor lcir :1'1it, 'and the motor'stops with the switch contacts ta, te and sb, 'se in closed position.With 'the 'contacts in this po- 'sition control electrode 3b of t'b'e 3is now connfected through switch cofritacts '619,15 to the oscillater'tube control ygrid I5y in the work circuit I. If the oscillator 'iso'atiri'g properly, a voltage is being 'produced (even though the workcircuit is not delivering any voltage) which is 'suiiicifent 'toreducetle 'plate current of tube 3 to 'the point where the relay 4becomes degener- `ized and contact 4a is permitted to lclose againstContact 4c.

With 'the contacts of the switch in the position rlast described, this'"deenergization of the fr'elay 4 closes the motor 'circuit and the motorbegins operation 'again and will continue to operate until the cam'segment Ba is moved sufficiently that lthe vswitch -B is actuated againtoclose 'its contacts 6a, "6d and 617,61. This action nowdisconnectsfcontrol `electrode 3b 'from the oscillater grid 15g Sand'restores it to rectifier and re- "s'istance 2, and if no voltage is'present 'therein the plate current of tube 3 will rise and the relayv 4will close its 'contact 4a against contact 4b, thereby again closing themotor circuit to con' tinue the tuning operation.

If switch 6 happens to have its contacts 6a, 6c and 6b, 6e closed wheninitial operations are attempted, as when the apparatus is first turnedon, as soon as tube 3 heats up and the oscillator begins to oscillateplate current in`r tube 3 drops because of the bias on its controlelectrode 3b; the motor circuit is closed by closure of the relaycontacts 4a and dcand the motor begins to opcrate the tuner. From hereon, the operation is as already described.

If, however, when the contacts of cam switch 6 are moved into uppercontact position and the control grid 3b connected tothe oscillatorcontrol grid, there is no voltage on the oscillator control grid (whichwould be the case if the tube had stopped oscillatingr due to adefective or missing crystal), the plate current of tube 3 would be ofsuiiicient value to hold contact 4a against contact 4b, thereby keepingthe motor circuit open. In other words, the operation of the circuit maybe summed up as follows:

Once during each tuning cycle, with the operation of the cam switch,tube 3 teststhe oscillating circuit, and if it is operating properly,the motor circuit is closed and operation continues, but if theoscillatoris not working, the motor circuitis opened and will remainopen until the trouble is found and remedied; so it will be seen thatshould trouble develop; i. e., should the oscillator tube burn out orshould the crystal become inoperative, the motor is prevented fromoperating. On the other hand, if the oscillator is functioning properly,operation of the motor continues through the next tuning cycle.

In the specification I have explained the prin# ciples of my inventionand the best mode in which I have contemplated applying those principlesso as to distinguish my invention from other inven# tions, and I haveparticularly pointed out and distinctly claimed the part, improvement,or combination which I claim as my invention or discovery. y

While I have shown and described certain preferred embodiments of myinvention, it will be understood that'modications and changes may bemade without departing from the spirit and scope of my invention, aswill be those skilled in the art.

Iclaim:

1. In automatic tuning apparatus, in combination, a frequencydetermining element, a work circuit including an oscillator fordelivering energy limited to -a frequency determined by said element,said work circuit having a variable tuning instrumentality poweroperated means for varying said tuning instrumentality, energyresponsive means for interrupting operation of said power means eitherin responseto delivery by said work circuit of a predetermined level ofenergy or in response to failure of the oscillator to deliver apredetermined level of energy, and means for periodically opera-tivelyassociating said energy responsive means alternately with said workcircuit and with said oscillator.

2. In automatic tuning apparatus, in combina.- tion, a frequencydetermining element, a work circuit including an oscillator fordelivering energy limited to a frequency determined by said element,said work circuit having a variable tunapparent to ving instrumentality,power means for varying said instrumentality, energy responsive meansfor 6 interrupting loperation of said-power means either in response todelivery by said'work circuit of a predetermined level of energy Vorinlresponse to failure of the oscillator totdeliver a predeterminedlevel of energy, and means for periodically operatively associating saidenergy responsive means alternately with said work circuit and with saidoscillator, said energy responsive means being arranged to beoperatively associated with said oscillator during a small part only ofeach tuning cycle. l ,y

3. In automatic tuning apparatus, in combination, a frequencydetermining element, va work circuit including van oscillator' fordelivering energy limited to a frequency determined by said element,said work circuit having a variable tuning instrumentality power'operated means for varying said tuning instrumentality, energyresponsive means for interrupting operation of said lpower means eitherin response to delivery by said work circuit of a predetermined level ofenergy or in response to failurel of the oscillator to deliver apredetermined level of energy, and means for periodically operativelyassociating said energy responsive means alternately with said workcircuit and with said oscillator, said energy responsive means beingarrangedtobeoperatively associated with said work circuit during themajor part of each tuning cycle and with said oscillator during a smallpart only 'of each tuning cycle;

4. In :automatic tuning apparatus, in combination, a frequencydetermining element, a work circuitv including anoscillator fordelivering energy limited to a frequency determined by said element,said work circuit having a variable tuning instrumentality, power meansfor varying said instrumentality, energy responsive means forinterrupting operation of said power means either in response todelivery by said work circuit of a predetermined levelv of energy orv inresponse to failure of the oscillator to deliver a predetermined levelvof energy, and means synchronized with said tuning instrumentality forperiodically and alternately connecting said energy responsive means -tosaid work circuit and to said oscillator.

5. In automatic tuning apparatus, in combination, afrequency-determining element, a work circuit including an oscillatorfor delivering energy limited to a frequency determined by said element,said work circuit having a variable tuning instrumentality, power meansfor varying said instrumentality, a power control circuit including athermionic vacuum tube having a current relay in the platecircuitthere'of having an' armature biased 'to'one contact position andclosable to another contact position by the current of said relay,and'acam actuated switchhaving at least .two contacts closable yinindividual ones of a rst and asecond operating positionof said switchand arranged in' circuit'with said power means and withsaid armature forYpreparing said power circuit for closure eitherin said'rst or saidsecond operating position of said cam switch, whereby closure'aridopening of said power circuit may be `controlled by'saidthermionic'relay, `and a lsecond set of contacts-on said cam switch andeffective in said rst and said second operating position thereof forselectively connecting the control electrode of said thermionic'vacuumtube to the output of said work circuit orto said oscillator, said camswitch being synchronized with said tuning instrumentality.

` 6. In automatic tuningapparatus; in combination, afrequency-determining elemerit,v a work 'circuit including anyoscillator. for :delivering enasentar.

elementsaid, work; circuit having a variable tun,-

ingv instrumentality; power means. for var-ying said instrumentality, apower control circuit including: athermionic vacuum tube having acurrent relay in the plate circuit thereof, said relay having anemmaturebiased to one contact position andA closable to4 another contactposition by the current of said relay; and a cam switch hav.- ing; arstset or iixed. and, movable contacts preparing said power controlcircuit for. closure. on either said one or said: other contactpositions of said' relay armature-andp a` second set of iixed andmovable: contacts for selectively connecting the control circuitoff-saidthermionic relay to the outputv f; said. work` circuit. or to saidoscillator respectively,` saidcam switch beingy synchronized with said'.tuning instrumentality, whereby in one positionV of; said canrswitch.predetermined current in said; relay causes closure of said powercircuit while in the other position of said cam switch predeterminedcurrent in said relay causes opening ci said power circuit.

7. In automatic tuningl apparatus, in combination, afrequency-determining elem-ent, a work circuit including an oscillatorfor delivering energy limited toA a frequency determined by saidelement, said work circuit having a variable tuning instrumentality,power means for Varying said instrumentality, a power control circuitincluding a thermionic, vacuum tube having a current, relay. the platecircuit thereof, said relay having an arnfiature-biasedV to one contactposition and closable to.v another contact position by the current ofsaid. relay, and a cam switchhaving a. rst. set of fixed and movablecontacts preparing said powerv control. circuit for closure on eithersaid one or said other. contact positions of said relay armature, and, asecond set of fixed and movable contacts forselectively connecting thecontrol circuit of said thermionic relay to the output. of said workcircuit or tosaid oscillator respectively, saidcamy switch being`synchronized with said tuning instrumentality, whereby in one positionof saidcam switch predetermined current insaid relay causes closure ofsaid power circuit while in the other position of said cam switch.predetermined current in said relay causes opening oi saidl powercircuit, said cam switch being arranged to prepare said powerA circuitfor closure through said other contact of said relay during the majorpart of the tun-ing cycle;

8. In automatic tuning apparatus, in combination, afrequency-determining element, a work circuit including an oscillatorfor deliveringr energylimited to a, frequency determined by saidelement, said work circuit havinga variable tuning instrumentality,power means for varying said instrumentality; apower control circuitincluding athe-rmienic vacuum tube. having a current relay in the platecircuit thereof, said relay having an armature biased to one contactposition l and closable to another contact position by the currentoffsaid relay, and a cam switch having a nrst set of fixed andmovablecontacts preparing said power control circuit for closure oneither said one or said other contact positions of said relay armature,and a second setr of' fixed and movable contacts for selectivelyconnecting the control circuit of said thermionic relay to the output ofsaid work circuit or to said oscillatorrespectively, said cam switchbeing synchronized with said tuning instrumentality, whereby in oneposition of said camy switch predetermined current in said relay causes.closure of` said power-circuit while in the other; position of saidcamswitch predetermined current in said relay causes opening of saidpower circuit, said cam 4 switch being arranged to prepare the powercircuit for closure on said one contact. of said relay during a smallpart only of each tuning cycle.

9, In automatic tuning apparatus, inl combination, afrequency-determining element, a work circuit including an oscillatorfor delivering energy limited to a frequency determined by said.element, said work circuit having a variable tuning instrumentality',power means for varying said instrumentality, a power contr-ol circuitincluding a thermionic vacuum tube havingA a current relay in the platecircuit thereof, said relay having anr armature biased to one contactposition and closablel to another contact position by the current ofsaid relay, and a cam switch having a rst setoi fixed and movablecontacts preparing said. power control circuit for closure on eithersaid one or said other contact positions of said relay armature, and asecond set of fixed and movable contacts for selectively connecting thecontrol circuit of said thermionic relay to the output of said workcircuit or to said oscillator respectively, saidcam switchy beingsynchronized with saidtuning instrumentality, whereby in one position ofsaid cam switch predetermined current in said relay causes closure ofsaid power circuit while in the other position of said cam switchpredetermined current in said relay causes opening of saidl powercircuit, said cam switch being arranged to prepare said power circuitfor closure through said other contact of said relay during the major'partY of the tuning cycle and for closure on said one contact of saidrelay during a small part onlyof each tuning cycle.

l0. Infautomatic tuning apparatus, in combination, afrequency-determining element, a work circuit including an oscillatorfor delivering energyhaving a frequency determined by said element,`said work circuit including a variable tuning instrumentality,powermeans for varying said instrumentality,l and a control system forcontrolling the energization of said power means, said system includingmeans operating in synchronized relation with said tuninginstrumentality for selectively coupling said control system during oneportion of each tuning cycle to the output of said Work circuit andduring another portion thereof to said oscillator, and means alsooperating in synchronized relation with said tuning instrumentality forreversing as between said one and said other portion of said each tuningcycle the mode of control effected by said control system over theenergization of said power means.

MADISON G. NICHOLSON, J n.

REFERENCES errno `The.l following references are of record in the le ofthis patent:

UNITED. S'IA'IESA PATENTS i Number Name Date 11,8971252 Gardner Feb. 14,1933 1,932,925 Chauveau Oct. 31, 1933 2,056,200 Lowell" Oct. 6, 19362,182,352 Prochnow Dec. 5, 1939 2,304,871 Andrews Dec. 15, 1942 FOREIGNPATENTS Number Country Date Great Britain Mar. 19, 1935

